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Dublin: 12 °C Sunday 26 October, 2014

Comet ISON will brush past the Sun at half 6 this evening, but will it survive?

The comet could simply melt due to the heat — or it could survive and light up our skies next month.

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At the time of this picture, Comet ISON was 97 million miles from Earth (AP Photo/NASA, Aaron Kingery)

ASTROPHYSICISTS ARE SPLIT over what will happen when the comet ISON passes near the sun, but a majority think it will break apart.

It is expected to get closest to the sun at 6.37pm this evening, however it probably won’t be visible from Earth except using NASA telescopes and spacecraft.

If ISON survives its passage near the Sun, it will be visible at night from December through February, crossing nearest Earth about 64 million kilometers away on December 26.

Since comets are just frozen balls of space dust left over from the formation of stars and planets billions of years ago, when one of them zips close to a hot star, like the Sun, sometimes the icy core simply melts.

“Many of us think it could break up into pieces, and some people think it won’t survive at all” after its brush near the Sun, said comet expert Carey Lisse of the Johns Hopkins Applied Physics Laboratory in the US, during a telephone press conference.

Some think it will survive

But he conceded, there are others who think the icy mass “will actually survive and come back out” on the other side of the sun, albeit somewhat shrunken down from its encounter with the Sun’s heat.

ISON will be just 1.17 million kilometers from the sun as it passes by where it will be hit by temperatures of around 2,700 degrees Celsius.

“I think it has a maybe 30 percent chance to make it” past the sun intact, Lisse said.

The comet “is like a loose snow ball,” he explained, saying it is “maybe half or a third water and it’s rather weak.” It’s also smaller than most comets, currently measuring around 1.2 kilometers in diameter.

“The average size for a comet is about three kilometers diameter, so this comet is maybe about half the size of the average, typical comet,” he said.

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In this frame grab taken from enhanced video made by NASA’s STEREO-A spacecraft, comet ISON is seen on the left as it approached the sun three day ago. A seperate comet, Encke, is seen just below ISON, the sun is to the right, just outside the frame. (AP Photo/NASA)

Either way it turns out, astronomers are watching keenly.

We “don’t really have any past experience we can use to judge or predict what is going to happen to this one,” said astrophysicist Karl Battams, of the Naval Research Laboratory in Washington, adding it’s “a very peculiar object but also a fascinating object”.

We have never seen a comet like this coming from the Oort cloud and going in the sun grazing orbit.

Scientists say the comet comes from the very origin of the solar system, 4.5 billion years ago, preserved “in deep freeze in the Oort cloud halfway to the next star for the last four and a half billion years,” Lisse said.

Additional reporting by Associated Press

© AFP 2013

Column: Eyes to the sky – Comet ISON might just be visible >

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